Healthy people are able to clear mucus secretions from their lungs by means of bi-directional airflow and a system of tiny hairlike follicles called “mucociliary escalators.” Airflow passing over the secretions creates shear forces that combine with the mucociliary escalators to transport mucus from the lower respiratory tract to upper airways. From there the secretions can be removed by coughing.
However, during illness a person's normal ability to remove secretions may become impaired. As the natural secretion clearance mechanism becomes more challenged, secretions may build up in the lungs, bronchial and tracheal passages creating a heightened potential for further exacerbation of illness. Retained mucus secretions in the warm, moist environment of the lungs create an excellent opportunity for the growth of bacteria. In addition, retained secretions may hinder the lungs' ability to exchange gas and increase the risk of pulmonary neoplasm. Keeping the lungs open and clear of secretions is integral to maintaining a healthy defense of the pulmonary system.
As the population ages, and the quality of air decreases, assaults on the respiratory system continue to rise. In addition to curable pulmonary infections, there are some 16 million people in the United States alone diagnosed with chronic lung disease, and it is estimated that an additional 16 million cases go undiagnosed. Associated costs in both healthcare and lost production hours are staggering.
Because of the rising costs associated with pulmonary disease and the importance of keeping the lungs clear, clinicians and patients alike seek simple, inexpensive therapy devices that can enhance secretion mobilization. However, despite the variety of devices available, few show evidence of overall benefit.
In the late 1970's a Swedish anesthesiologist pioneered the use of “high-frequency ventilation” for life support by programming a ventilator to deliver 60 breaths per minute, or 1 hertz. Subsequently the application of high-frequency delivery of gas to the airways was found to show favorable results in mobilizing secretions, especially when combined with medicated aerosol. While exact mechanisms of this therapy are not fully understood, it is likely that, as the column of air in the airways is oscillated by the high-frequency pulses of gas, the viscosity of the mucus is reduced by the untangling of some of the larger molecule strands, such as DNA and F-actin, which tend to be present as a byproduct of infection. Additionally, the high-frequency, intermittent delivery of gas contributes to a bi-directional flow creating wind shear forces which, in turn, help to mobilize the secretions in a cephalad fashion. However, in spite of therapeutic promise, the vast majority of those in need of this therapy do not have access to it because current technology is too complex and, therefore, ultimately too expensive.
U.S. Pat. Nos. 4,592,349, 4,805,613, 4,838,260, 4,930,501, 5,007,420, 5,116,088, 5,165,398, and 5,862,802 describe ventilators that combine high-frequency oscillation gas flow with aerosol. However, because these ventilators are designed primarily for life support, they connect to the patient via patient adapters that incorporate relatively complex mechanized valves that open and close between phasic shifts from inhalation to exhalation.
U.S. Pat. No. 4,592,349 describes a “pneumatic clutching means” as an exhalation valve assembly with a venturi slidably mounted within in such a way as to move between open and closed positions. Although highly effective in delivering life-support ventilation, the sliding venturi patient adapter is too complex, bulky, and costly to manufacture to be included in a simple, inexpensive therapy device. The patient interface necessitates the fabrication of a number of moving parts made of a variety of materials. The resulting friction of the constant sliding between open and closed positions eventually fatigues valve components that must be replaced. Additionally, the sliding venturi patient interface requires critical dimensions that prevent a reduction in its size and weight.
Although an alternate embodiment of a patient adaptor to be used with the above devices described in U.S. Pat. No. 4,592,349 utilizes a fixed venturi, it, nonetheless, must incorporate or attach to a mechanical exhalation valve that opens and closes between inhalation and exhalation. This design, again, although effective in delivering life-support ventilation, renders the patient connector too complex and costly to be used in a simple, inexpensive breathing therapy device.
In addition to being expensive because of their complexity of manufacturing and maintenance, the devices currently capable of delivering high-frequency oscillatory therapy to the lungs are complicated and difficult to use. They require either significant training of the patient or a trained professional to administer the therapy. U.S. Pat. No. 4,592,349, cited above, also describes a simpler version of these life-support ventilators which is specifically intended for therapeutic use. However, even this simpler, scaled-down version is designed with a mechanism to terminate the delivery of gas during exhalation, as well as adjustments for both pressure and pulse frequency during a therapy session. This design renders the device both costly to manufacture and complex to use.